Photic stimulation comprises application of radiant energy to an organism at a frequency and intensity to which an organism will respond. Photic stimulation varies in its effect depending on wavelength, intensity and manner of application. Low intensity photic stimulation may be used for therapeutic purposes. However, high intensity photic stimulation may be used to apply non-lethal force having a disabling effect on humans or animals, who may be referred to as target subjects. High intensity light sources are incorporated in non-lethal weapons. “High intensity” in this context has an established meaning in the art both as to level of stimulation and as to light intensity. The stimulation is generally received by the eyes and interpreted through various mechanisms in the brain.
In civil unrest situations, peace officers may have an urgent need to quickly disable individuals or groups of people. Individuals or crowds can cause significant property damage and injury or death to others. However, the urgency of restoring order does not outweigh the undesirability of the use of deadly force on the civilian population. Therefore, use of high intensity light systems is highly desirable to produce disabling effects. High intensity light sources can cause “flash blindness,” which is temporary vision impairment. Recovery can take minutes to hours. Afterimages may remain for hours or days. Other effects triggered in response to high intensity photic stimulation include distraction, aversion, confusion, disorientation, fear and nausea. Strobe lights can also cause seizures to debilitate target subjects who are epileptogenic.
Users employing photic stimulation systems need to be protected from the system's effects. Using dark, neutral density goggles to reduce light reaching a user's eyes is undesirable as a measure to reduce the effect of the flashing light. The user's ability to see the when the light is not flashing may be severely limited, or if the user adapts to the dark filter, the resulting dilation of pupils in the eyes will render the user more susceptible to the light flashes because no time is provided for the eyes to adjust quickly to changing light levels.
Use of laser and non-laser light sources is reviewed in T. Donnelly, Less Lethal Technologies —Initial Prioritisation and Evaluation Publication No. 12/01, (Police Scientific Development Branch, Home Office Policing And Crime Reduction Group, Hertfordshire, UK, 2001). It is pointed out that laser light may cause skin damage as well as permanent eye injury. A device that dazzles at a long range may cause permanent damage at short range. Prior art devices are described which use lasers providing 100–500 mW output power. Damage is more likely when the laser light is used at night, when a target subject's pupil may have a nominal diameter of 7 mm. In daytime, a target subject's nominal pupil diameter is 2 mm. Consequently, the pupil will admit approximately ten times as much light to the retina at night as in the daytime.
Another shortcoming of laser systems is that use of laser-based devices to cause blindness violates international law. The Convention On Prohibitions Or Restrictions On The Use Of Certain Conventional Weapons Which May Be Deemed To Be Excessively Injurious Or To Have Indiscriminate Effects (1980), particularly Protocol IV, Protocol Relating to Blinding Laser Weapons (1995), (International Committee of the Red Cross, Geneva, Switzerland), prohibits the use of laser weapons causing blindness to the naked eye or eye with corrective lenses.
A number of prior systems exist for purpose of disabling of target subjects with flashing light. U.S. Pat. No. 6,367,943 discloses a shield combined with light sources which produce light pulses. The light pulses are directed to disable a target subject whom the user of the shield wishes to capture or control. The light sources comprise lasers or light emitting diodes (LEDs). These sources have particular frequencies of light emission. The patent points out that if the target subjects are aware of the value of the frequency used in standard equipment, they can employ laser goggles to block the light pulses. In one form, light sources of two different frequencies are utilized, since two frequencies cannot easily be locked by wearing laser goggles. Providing for two different wavelengths of light increases cost and complexity of the system. Additionally, the laser embodiments of this system are subject to the drawbacks of laser systems as described above.
U.S. Pat. No. 6,767,108 discloses a flash grenade comprising a layer of flash lamps mounted in a cylindrical housing. Light flashes are intended to disable hostages or non-combatants as well as perpetrators. A trigger circuit for the flash lamps is included in the grenade. There is no opportunity to remotely control the ignition of the flash lamps.
U.S. Pat. No. 5,072,342 discloses a hand-held pulsed light focused by a reflector and mounted in a simulated gun. A user points the gun at an assailant's head for the purpose of causing temporary blindness. This apparatus has a limited field of illumination, and is not suited for a user facing a number of assailants.
The above-described prior art systems do not place any particular emphasis on protecting the user who is employing the system from the effects of high intensity flashing illumination. The user may be disabled as well as the target. Even when a high intensity light source is pointed in a direction away from a user, a user could be subjected to some degree of disability or immobilization from reflected light. Also, when one user is directing the high intensity light at target subjects, there may also be other users present in the field of illumination. Consequently friend as well as foe may be disabled.
An alternative to laser goggles is seen in U.S. Pat. No. 5,756,989, which discloses color night vision goggles using an image intensifier to amplify input radiant energy from a low-luminance field of view. A “bright source detector” is used to detect incoming radiation from a laser jamming system. Output pulses gate the image intensifier to disable the image intensifier in synchronism with laser jamming pulses. The system is independent of the jamming signal. It cannot be synchronized with the jamming signal, but must operate in response to receipt of the jamming signal. The system must account for lag time in responding to the beginning and end of incoming jamming pulses.
U.S. Pat. No. 5,081,542 discloses an eye protection device including a liquid crystal light valve which provides a user an image of a scene. The light valve comprises a mechanism for absorbing energy from a laser threat directed at the user. However, the light valve cannot simply turn substantially opaque to block incoming radiation.